Electric supply systems are known in the automotive field, which may include several components, such as, for example: alternators, voltage regulators, rectifier diode bridges, and a battery. An alternator, which converts mechanical energy into electric power, includes a rotor, equipped with a coil and three stators, equipped with other coils. The rotor coil is energized with an electric current from a power transistor, and the electric power generated by the alternator is supplied by the rectifier bridge to electric loads of the motor vehicle, or it is used to restore the charge status of the battery. In driving other inductive-type loads (for example, the throttle motor) of a motor vehicle, the use of an H-bridge circuit is known.
In such a type of driving, an undesired condition can occur, wherein the load coil is incorrectly connected to the relative driving circuit, or it even separates therefrom, compromising the charge of the battery or the load supply to the motor vehicle. Such a condition, which is called “open load” condition, corresponds to a situation wherein the electrical current concerning that coil is null or much lower than the one normally present.
Two diagnostic methods for determining open load condition are known. According to a first method, the detection of the open load condition is carried out by directly measuring the current concerning the load, employing a sensing resistor and an operational amplifier. According to another indirect measuring method, an estimation of the current in the load is carried out by employing a current mirror and an additional driving circuit, which is a copy of the one actually driving the load. Prior art methods for detecting the incorrectly connected load condition are generally not satisfactory because of additional leakage introduced in the circuit and the circuit complexity required for their implementation.